Speech is the ability that is given only to humanity. Biped locomotion had changed the form of mouth and throat, which enlarged cerebrum. Language is the means of thinking as well as communication. We learn language to use it not only in our daily life, but also in studying. There are some causes of delay in speech development : hearing disturbance, intellectual deficiency, autism, cerebral palsy, and so on. As there is the critical period, it is important to find the cause and deal with it soon. To promote speech development, both stable everyday life and positive direction are necessary.